As the volume of portable electronic device is gradually reduced, a touch panel display module having an input function and a display function is widely used in the small-sized portable electronic device such as a mobile phone, a personal digital assistant (PDA), a smart phone and the like. FIG. 1 is a schematic cross-sectional view illustrating a touch panel display module according to the prior art. As shown in FIG. 1, the touch panel display module 1 principally comprises a transparent touch panel 10 and a flat display 11. The touch panel 10 is a resistive touch panel. The touch panel 10 comprises a layer of transparent conductive film 101 and a layer of transparent conductive substrate 102. There is a constant voltage difference between the transparent conductive film 101 and the transparent conductive substrate 102. In addition, many spacer dots 103 are interposed between the transparent conductive film 101 and the transparent conductive substrate 102 for isolation between these two layers. When a finger or stylus touches the touch panel display module 1, the transparent conductive film 101 (top layer) is deformed and contacted with the transparent conductive substrate 102 (bottom layer). As such, two analog voltage values indicative of the touched position is transmitted to an analog-to-digital converter 104. The analog voltage values are converted into digital signals by the analog-to-digital converter 104. The digital signals are transmitted to a back-end microprocessor 105. The digital signals are processed by the back-end microprocessor 105, thereby obtaining the coordinate values (X, Y) of the touched position.
The resistive touch panel, however, has some drawbacks. For example, if the transparent conductive film 101 is seriously scratched, the resistive touch panel 10 is possibly subject to a broken circuit and thus the resistive touch panel 10 fails to be normally operated. Moreover, the resistive touch panel has inferior optical properties and low touch sensitivity.
For solving the drawbacks encountered from the resistive touch panel, a capacitive touch panel has been proposed and widely used in various electronic devices. FIGS. 2A and 2B are schematic views illustrating a conventional capacitive touch panel. A first set of transparent electrodes 22 and a second set of transparent electrodes 23 are disposed on a substrate 21 and orthogonal to each other. The capacitance values of the transparent electrodes 22 and 23 are periodically detected by an X input sensor 26 and a Y input sensor 28. When a finger or stylus touches the capacitive touch panel 2, the capacitance value sensed by the X input sensor 26 and the Y input sensor 28 is changed. The sensed capacitance values indicative of the touched position are transmitted to the computing unit 29, thereby obtaining the coordinate values (X, Y) and the pressure level Z of the finger on the touched position. For increasing the scratch resistance of the capacitive touch panel 2, a silicon dioxide insulating layer 20 is usually disposed on the external surface of the capacitive touch panel 2. The related contents of the capacitive touch panel are disclosed in for example U.S. Pat. No. 5,914,465.
Generally, the conventional capacitive touch panel 2 only responds to finger contact but does not work with a stylus because the contact point of the stylus is much smaller than that of the human finger. For detecting the position of the contact point of the stylus, the transparent electrodes 22 and 23 in the orthogonal arrangement should be closely spaced. Under this circumstance, the capacitive touch panel 2 needs to have more pins to be connected to the X input sensor 26 and the Y input sensor 28. As the number of pins is increased, the space for accommodating the pins is increased, the fabricating cost is increased and the sensing time period is extended. Moreover, even if the capacitive touch panel 2 is designed to only respond to finger contact, the capacitive touch panel 2 is not aesthetically pleasing because the transparent electrodes 22 and 23 in the orthogonal arrangement are relatively far spaced. In other words, if the distance between the adjacent electrodes 22 and 23 is too long, the image quality is deteriorated.
Therefore, there is a need of providing an improved object position detecting device so as to obviate the drawbacks encountered from the prior art.